Consistency measuring apparatus responsive to motor current



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y mns/won BY William R. Lewis ATTORNEYS Patented Oct. 6, 1953 CONSISTENCY AMEASURING APPARATUS RESPONSIVE .'-IO MOTOR CURRENT William sR. 'Lew'is, 7Kansas City, tM0., assignorto 0.-:1. APatterson Company, a corporation Iof :Missouri ApplicationNovemher 23,.1949,.Serial No. 128,942

(Cl. 'S18- 490) '.7 Claims. l

'This `invention relatesto an 'instrument for-*determining the consistency 'of materials. YIt 'is `a modification of 'the instrument described uand claimed in the co-pending application 'of Charles 'H.`Ki1nball and William R. Lewis for Consistency Determination, S. N. 57,066, Vfiled October 28, 1948.

*In said prorapp'lication itis shown'that-curves Ican vbe obtained which represent the lconsistency of Ya lmaterial 'by continuously plotting vvalues taken Vfrom Athe differential in current Yor power yrequirements for mixing -a material over Ysmall vincrements of time.

An object of this invention is to simplify and improve'uponthe means for obtaining'integrate'd I.va-lues proportional -`to the power requirements in the stirring ormixing'of materials. 11i-'further obect is to produce a sensitive -but 'rugged instru- .sistency values.

'The :instrument is constructed lto takeadvantage 'of the fact that current variations -in -the lpower required to stir or mix .a .material can :be

used'to show proportional variations in the power. When the consistency of a material changes while being stirred, the mixing blades are intermittently freed from the mix in cycles known as impact cycles having a substantially constant time period. The current required to actuate `the mixing blades is a value indicative of the consistency of the material, and the rate of change in current between successive cycles can be employed as a measurement of consistency. 'I'his rate of current change, or current slope, can be obtained from the power required to stir the material. In an A. C. power supply to the stirring motor, the power equals the product of the voltage, current and power factor. The voltage is normally constant with reasonable limits, and the variations in the power factor are negligible. Therefore variations in the power are observed from current variations. By means of filter circuits and a recorder, such current Variations are proportionally reproduced in the from of a smooth curve which may either represent the change per unit of time in the consistency of a material as it is being stirred, or a static consistency value which may be compared with a previously derived standard.

'ment Awhich does not require the use of vacuum Y The means by which .these and other objects of the invention are obtained rare more fully described .with referencetothe.accompanying drawings, in which:

Figure '1 is an electrical diagram of the .instrument.;

Figure '2 'is afgraph ofthe current supplied by 'the power line.;

`Figure 3 is agraph-,o'f the current after "a portion of the cycle has 'been 'ltered therefrom;

.Figure 4 is a graph Vof cthe curve of Figure 3 after 'the power 'line 'frequency has Abeen Tfiltered from the current; .and

Figure 5 'is a graph ofthe smooth curve produced 'by differentiating the current'into 4anonpulsating direct current.

In Figure '1, `motor '2, which serves -to rdrive the blades .of a mixer or stirrerfis -fed by power line '4,having-alterna'ting currentfa substantially'con- 'stant voltage, anda negligible power factor. Current 'transformer iB, shown as a'toroi'd coil on one leg of power line '4, :conducts a current proportional to the power line Ycurrent to 'rectifier '8, preferablya selenium rectifier, Aand resistance 1i). The alternating rcurrent .from coil l "is lof 'thefrevquency ofpower line #,plu's ahigher or'lower frequency component .caused "by variations 'in the load on motor 2, such being the 4current at point A, said current having the ,graphical form illus- Atratedinligurez.

The A. C. power current curve is modulated by the variation in load requirements into cycles t1, t2, t3, etc., which represent the impact cycles as the mixer blades reengaged the material after being momentarily freed therefrom.

Rectifier 8 cuts off a portion of the current curve, so that only positive or negative values of the current are passed through. Thus in Figure 3 only the positive values of the curve of Figure 2, as exist at point B in Figure l, are illustrated as being passed by rectifier 8, these values having the zero line for a base. Other base positions can be selected as well understood in the art.

By reason of stabilizing resistance I0, a small current is passed to a lter system I l composed of condenser I2, choke I4 and condenser I6, the power line frequency being filtered out so that at point C, Figure 1, the current takes the graphical form of Figure 4. Thus the current passed to condenser !8 varies proportionately with load current variations in power line 4.

Condenser I8 and resistance 2u in series form a differentiating circuit 2 I. The current through this circuit develops a Voltage across resistor 20 which is proportional to the rate of change of the current impressed on the circuit. It is to be noted that the power frequency of Figure 2 does not appear. The curve of Figure 4 does appear and corresponds to the forward slopes y, and .e of each impact cycle which is used to develop a corresponding voltage at point D, Figure 1. The successive voltages at D are represented by the substantially smooth curve D in Figure 5. This voltage changes with changes in the consistency of the mix.

The voltage at point D, Figure 1, is then passed through a rectier 22 to a measuring network of condenser 24 in parallel with a voltmeter 28 and/or recorder 30. Rectifier 22 prevents condenser 24 from discharging into resistor 2li when the voltage of point D is decreasing. Condenser 24 acts as a part of an integrating circuit with a short-time constant so the voltmeter 28 remains steady during sub-transient conditions. Thus the smooth curve of Figure 5 can be reproduced on the recorder 3B.

The described circuit is of simple and rugged construction, and no vacuum tubes are needed to obtain a non-pulsating direct current which is proportional to the power required to drive the mixing or stirring motor.

VIn substance, this device simply consists of a toroid coil or current transformer, a half-wave rectifier, a lter, a differentiating circuit, and a recording instrument having a blocking rectiiier and short-time integration.

Having now described the means by which the objects of the invention are obtained, I claim:

l. A consistency measuring instrument for indicating relative values obtained from the Velectrical power supplied to a stirring motor, comprising means for producing an alternating current proportional to the current in the power supply to a stirring motor, means receiving said proportional alternating current for eliminating the power supply frequency from said proportional alternating current and permitting a second frequency produced by variations in the load requirements of the motor, and means responsive to said second frequency for diierentiating the impulses of said second frequency and producing a non-pulsating direct current proportional to the load variations on the stirring motor.

2. A consistency measuring instrument as in '4 claim 1, further comprising means coupled to said responsive means for integrating the differential values of said second frequency into a direct current.

3. A consistency measuring instrument as in claim 2, said means for producing an alternating current comprising a circuit composed of a current transformer connected in series with a selenium rectifier and a resistor.

4. A consistency measuring instrument as in claim 3, said means for eliminating the power supply frequency comprising a filter circuit composed of a first condenser, a choke coil and a second condenser.

5. A consistency measuring instrument as in claim 4, said differentiating means comprising a condenser and a resistor in series with said power supply frequency eliminating means and connected across said filter circuit.

6. A consistency measuring instrument as in claim 5, said integrating means comprising a circuit having a rectifier, and a condenser in parallel with said resistor of said differentiating means through said rectifier.

7. A consistency measuring apparatus comprising a stirring motor, an alternating electric current source, means connecting said source to said motor, means coupled to said connecting means for producing an alternating current proportional to the current supplied to said motor, means receiving said proportional alternating current for eliminating the power supply frequency from said proportional alternating currentand permitting a second frequency produced by variations in the load requirements of said motor, and means responsive to said second frequency for differentiating the impulses of said second frequency and producing a non-pulsating direct current proportional to the load variations on said motor.

WILLIAM R. LEWIS.

References Cited in the le of this patent UNITED STATES PATENTS Lord Aug. 25, 198,6 

